Some construction machines are furnished with a battery and have electric power stored in the battery converted to motive power. The construction machines of this type include a battery-driven hydraulic shovel (battery shovel) having a battery and a motor in place of the engine so that the motor drives a hydraulic pump to operate a hydraulic actuator; a hybrid hydraulic shovel equipped with an engine, a battery, and a generator motor; and a wheel loader and a dump truck each getting the electric power of a battery to drive a traction motor.
The battery mounted on this type of construction machine provides large-capacity output and is expensive but permits lower energy output per unit weight than kerosene that is used to drive the engine. This poses a big challenge: how to increase the amount of work and extend operation hours by effectively utilizing a limited-capacity battery that can be mounted onboard the machine.
One construction machine taking the above aspect into account has an inverter device mounted onboard thereby to calculate an amount of electric power stored in an onboard battery so that if the amount of electric power is determined to be low, the maximum output of an onboard electric actuator is reduced (see JP-2009-197514-A). That is, before and after the amount of electric power is determined to be low, this technique involves the use of a plurality of modes for limiting battery output (the modes may be called the power-limited modes hereunder where appropriate). Another technique, related not to construction machines but to electric vehicles, involves getting an onboard controller to calculate the amount of electric power (Wh) stored in an onboard battery so that the calculated amount of electric power is displayed on a display device (see JP-8-201488-A).